The small heath is a small butterfly while a meadow brown is quite a large butterfly. As far as I know butterflies don't usually vary much in size within a species - not to the extent that you can confuse these two.From the photo the size of this butterfly is right for a small heath.

Furthermore, with the butterfly back-lit there appears to be a semi-transparent patch on the hind wing between the darker inner part and the lighter outer part. If you look closely at the photo in the link that emg supplied you can see a lighter patch of the same shape. I can't see anything like that in the photo of the meadow brown in my butterfly field guide.